For people who are wondering whether "magic_quotes_gpc" has any affect on "filter_input" operation, here is an extract from a PHP source file:

* As the input filter acts on input data before the magic quotes function mangles data, all access through the filter() function will not have any quotes or slashes added - it will be the pure data as send by the browser.

So when using this function, there is no need to strip the slashes when "magic_quotes_gpc" is enabled.